Cooling system for high density heat load

ABSTRACT

A cooling system for transferring heat from a heat load to an environment has a volatile working fluid. The cooling system includes first and second cooling cycles that are thermally connected to the first cooling cycle. The first cooling cycle is not a vapor compression cycle and includes a pump, an air-to-fluid heat exchanger, and a fluid-to-fluid heat exchanger. The second cooling cycle can include a chilled water system for transferring heat from the fluid-to-fluid heat exchanger to the environment. Alternatively, the second cooling cycle can include a vapor compression system for transferring heat from the fluid-to-fluid heat exchanger to the environment.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/607,934, filed Sep. 10, 2012, which is a continuation of U.S.application Ser. No. 10/904,889, filed Dec. 2, 2004, which claims thebenefit of U.S. Provisional Patent Application Ser. No. 60/527,527,filed Dec. 5, 2003, each of which are incorporated by reference.

BACKGROUND

The present disclosure generally relates to cooling systems, and moreparticularly, to a cooling system for a high density heat load.

Electronic equipment in a critical space, such as a computer room ortelecommunications room, requires precise, reliable control of roomtemperature, humidity, and airflow. Excessive heat or humidity candamage or impair the operation of computer systems and other components.For this reason, precision cooling systems are operated to providecooling in these situations. However, problems may occur when coolingsuch high density heat loads using a direct expansion (DX) coolingsystem. Existing DX systems for high-density loads monitor airtemperatures and other variables to control the cooling capacity of thesystem in response to load changes. Thus, existing DX systems requirerather sophisticated controls, temperature sensors, and other controlcomponents. Therefore, a need exists for a cooling system that isresponsive to varying density heat loads and that requires less controlof valves and other system components. Moreover, conventional computerroom air conditioning systems require excessive floor space for managinghigh-density heat loads. The present disclosure is directed toovercoming, or at least reducing the effects of, one or more of theproblems set forth above.

SUMMARY

A cooling system is disclosed for transferring heat from a heat load toan environment. The cooling system has a working fluid, which is avolatile working fluid in exemplary embodiments. The cooling systemincludes first and second cooling cycles that are thermally connected toone another. The first cooling cycle includes a pump, a first heatexchanger, and a second heat exchanger.

The first heat exchanger is in fluid communication with the pump throughpiping and is in thermal communication with the heat load, which may bea computer room, electronics enclosure, or other space. The first heatexchanger can be an air-to-fluid heat exchanger, for example. Inaddition, a flow regulator can be positioned between the pump and thefirst heat exchanger.

The second heat exchanger includes first and second fluid paths inthermal communication with one another. The second heat exchanger can bea fluid-to-fluid heat exchanger, for example. The first fluid path forthe working fluid of the cooling system connects the first heatexchanger to the pump. The second fluid path forms part of the secondcooling cycle.

In one embodiment of the disclosed cooling system, the second coolingcycle includes a chilled water system in thermal communication with theenvironment. In another embodiment of the disclosed cooling system, thesecond cooling cycle includes a refrigeration system in thermalcommunication with the environment. The refrigeration system can includea compressor, a condenser, and an expansion device. The compressor is influid communication with one end of the second fluid path of the secondheat exchanger. The condenser, which can be an air-to-fluid heatexchanger, is in fluid communication with the environment. The condenserhas an inlet connected to the compressor and has an outlet connected toanother end of the second fluid path through the second heat exchanger.The expansion device is positioned between the outlet of the condenserand the other end of the second fluid path.

The foregoing summary is not intended to summarize each potentialembodiment or every aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, a preferred embodiment, and other aspects of thesubject matter of the present disclosure will be best understood withreference to the following detailed description of specific embodimentswhen read in conjunction with the accompanying drawings, in which:

FIG. 1 schematically illustrates one embodiment of a cooling systemaccording to certain teachings of the present disclosure.

FIG. 2 schematically illustrates another embodiment of a cooling systemaccording to certain teachings of the present disclosure.

FIG. 3 illustrates a cycle diagram of the disclosed cooling system.

FIG. 4 illustrates a cycle diagram of a typical vapor compressionrefrigeration system.

While the disclosed cooling system is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are described herein indetail. The figures and written description are not intended to limitthe scope of the inventive concepts in any manner. Rather, the figuresand written description are provided to illustrate the inventiveconcepts to a person of ordinary skill in the art by reference toparticular embodiments.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, the disclosed cooling system 10 includes afirst cooling cycle 12 in thermal communication with a second cycle 14.The disclosed cooling system 10 also includes a control system 100. Boththe first and second cycles 12 and 14 include independent workingfluids. The working fluid in the first cycle is any volatile fluidsuitable for use as a conventional refrigerant, including but notlimited to chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), orhydrochloro-fluorocarbons (HCFCs). Use of a volatile working fluideliminates the need for using water located above sensitive equipment,as is sometimes done in conventional systems for cooling computer room.The first cycle 12 includes a pump 20, one or more first heat exchangers(evaporators) 30, a second heat exchanger 40, and piping to interconnectthe various components of the first cycle 12. The first cycle 12 is nota vapor compression refrigeration system. Instead, the first cycle 12uses the pump 20 instead of a compressor to circulate a volatile workingfluid for removing heat from a heat load. The pump 20 is preferablycapable of pumping the volatile working fluid throughout the firstcooling cycle 12 and is preferably controlled by the control system 100.

The first heat exchanger 30 is an air-to-fluid heat exchanger thatremoves heat from the heat load (not shown) to the first working fluidas the first working fluid passes through the first fluid path in firstheat exchanger 30. For example, the air-to-fluid heat exchanger 30 caninclude a plurality of tubes for the working fluid arranged to allowwarm air to pass therebetween. It will be appreciated that a number ofair-to-fluid heat exchangers known in the art can be used with thedisclosed cooling system 10. A flow regulator 32 can be connectedbetween the piping 22 and the inlet of the evaporator 30 to regulate theflow of working fluid into the evaporator 30. The flow regulator 32 canbe a solenoid valve or other type of device for regulating flow in thecooling system 10. The flow regulator 32 preferably maintains a constantoutput flow independent of the inlet pressure over the operatingpressure range of the system. In the embodiment of FIGS. 1 and 2, thefirst cycle 12 includes a plurality of evaporators 30 and flowregulators 32 connected to the piping 22. However, the disclosed systemcan have one or more than one evaporator 30 and flow regulators 32connected to the piping 22.

The second heat exchanger 40 is a fluid-to-fluid heat exchanger thattransfers the heat from the first working fluid to the second cycle 14.It will be appreciated that a number of fluid-to-fluid heat exchangersknown in the art can be used with the disclosed cooling system 10. Forexample, the fluid-to-fluid heat exchanger 40 can include a plurality oftubes for one fluid positioned in a chamber or shell containing thesecond fluid. A coaxial (“tube-in-tube”) exchanger would also besuitable. In certain embodiments, it is preferred to use a plate heatexchanger. The first cycle 12 can also include a receiver 50 connectedto the outlet piping 46 of the second heat exchanger 40 by a bypass line52. The receiver 50 may store and accumulate the working fluid in thefirst cycle 12 to allow for changes in the temperature and heat load.

In one embodiment, the air-to-fluid heat exchanger 30 can be used tocool a room holding computer equipment. For example, a fan 34 can drawair from the room (heat load) through the heat exchanger 30 where thefirst working fluid absorbs heat from the air. In another embodiment,the air-to-fluid heat exchanger 30 can be used to directly remove heatfrom electronic equipment (heat load) that generates the heat bymounting the heat exchanger 30 on or close to the equipment. Forexample, electronic equipment is typically contained in an enclosure(not shown). The heat exchanger 30 can mount to the enclosure, and fans34 can draw air from the enclosure through the heat exchanger 30.Alternatively, the first exchanger 30 may be in direct thermal contactwith the heat source (e.g. a cold plate). It will be appreciated bythose skilled in the art that the heat transfer rates, sizes, and otherdesign variables of the components of the disclosed cooling system 10depend on the size of the disclosed cooling system 10, the magnitude ofthe heat load to be managed, and on other details of the particularimplementation.

In the embodiment of the disclosed cooling system 10 depicted in FIG. 1,the second cycle 14 includes a chilled water cycle 60 connected to thefluid-to-fluid heat exchanger 40 of the first cycle 12. In particular,the second heat exchanger 40 has first and second portions or fluidpaths 42 and 44 in thermal communication with one another. The firstpath 42 for the volatile working fluid is connected between the firstheat exchanger 30 and the pump. The second fluid path 44 is connected tothe chilled water cycle 60. The chilled water cycle 60 may be similar tothose known in the art. The chilled water system 60 includes a secondworking fluid that absorbs heat from the first working fluid passingthrough the fluid-to-fluid heat exchanger 40. The second working fluidis then chilled by techniques known in the art for a conventionalchilled water cycle. In general, the second working fluid can be eithervolatile or non-volatile. For example, in the embodiment of FIG. 1, thesecond working fluid can be water, glycol or mixtures thereof.Therefore, the embodiment of the first cycle 12 in FIG. 1 can beconstructed as an independent unit that houses the pump 20, air-to-fluidheat exchanger 30, and fluid-to-fluid heat exchanger 40 and can beconnected to an existing chilled water service that is available in thebuilding housing the equipment to be cooled, for example.

In the embodiment of the disclosed cooling system 10 in FIG. 2, thefirst cycle 12 is substantially the same as that described above.However, the second cycle 14 includes a vapor compression refrigerationsystem 70 connected to the second portion or flow path 44 of heatexchanger 40 of the first cycle 12. Instead of using chilled water toremove the heat from the first cycle 12 as in the embodiment of FIG. 1,the refrigeration system 70 in FIG. 2 is directly connected to or is the“other half” of the fluid-to-fluid heat exchanger 40. The vaporcompression refrigeration system 70 can be substantially similar tothose known in the art. An exemplary vapor compression refrigerationsystem 70 includes a compressor 74, a condenser 76, and an expansiondevice 78. Piping 72 connects these components to one another and to thesecond flow path 44 of the heat exchanger 40.

The vapor compression refrigeration system 70 removes heat from thefirst working fluid passing through the second heat exchanger 40 byabsorbing heat from the exchanger 40 with a second working fluid andexpelling that heat to the environment (not shown). The second workingfluid can be either volatile or non-volatile. For example, in theembodiment of FIG. 2, the second working fluid can be any conventionalchemical refrigerant, including but not limited to chlorofluorocarbons(CFCs), hydrofluorocarbons (HFCs), or hydrochloro-fluorocarbons (HCFCs).The expansion device 78 can be a valve, orifice or other apparatus knownto those skilled in the art to produce a pressure drop in the workingfluid passing therethrough. The compressor 74 can be any type ofcompressor known in the art to be suitable for refrigerant service suchas reciprocating compressors, scroll compressors, or the like. In theembodiment depicted in FIG. 2, the cooling system 10 is self-contained.For example, the vapor compression refrigeration system 70 can be partof a single unit that also houses pump 20 and fluid-to-fluid heatexchanger 30.

During operation of the disclosed system, pump 20 moves the workingfluid via piping 22 to the air-to-fluid heat exchanger 30. Pumpingincreases the pressure of the working fluid, while its enthalpy remainssubstantially the same. (See leg 80 of the cycle diagram in FIG. 3). Thepumped working fluid can then enter the air-to-fluid heat exchanger orevaporator 30 of the first cycle 12. A fan 34 can draw air from the heatload through the heat exchanger 30. As the warm air from the heat load(not shown) enters the air-to-fluid heat exchanger 30, the volatileworking fluid absorbs the heat. As the fluid warms through the heatexchanger, some of the volatile working fluid will evaporate. (See leg82 of the cycle diagram in FIG. 3). In a fully loaded system 10, thefluid leaving the first heat exchanger 30 will be a saturated vapor. Thevapor flows from the heat exchanger 30 through the piping 36 to thefluid-to-fluid heat exchanger 40. In the piping or return line 36, theworking fluid is in the vapor state, and the pressure of the fluid dropswhile its enthalpy remains substantially constant. (See leg 84 of thecycle diagram in FIG. 3). At the fluid-to-fluid heat exchanger 40, thevapor in the first fluid path 42 is condensed by transferring heat tothe second, colder fluid of the second cycle 12 in the second fluid path44. (See leg 86 of the cycle diagram in FIG. 3). The condensed workingfluid leaves the heat exchanger 40 via piping 44 and enters the pump 20,where the first cycle 12 can be repeated.

The second cooling cycle 14 operates in conjunction with first cycle 12to remove heat from the first cycle 12 by absorbing the heat from thefirst working fluid into the second working fluid and rejecting the heatto the environment (not shown). As noted above, the second cycle 14 caninclude a chilled water system 60 as shown in FIG. 1 or a vaporcompression refrigeration system 70 as shown in FIG. 2. During operationof chilled water system 60 in FIG. 1, for example, a second workingfluid can flow through the second fluid path 44 of heat exchanger 40 andcan be cooled in a water tower (not shown). During operation ofrefrigeration system 70 in FIG. 2, for example, the second working fluidpasses through the second portion 44 of fluid-to-fluid heat exchanger 40and absorbs heat from the volatile fluid in the first cycle 12. Theworking fluid evaporates in the process. (See leg 92 of the typicalvapor-compression refrigeration cycle depicted in FIG. 4). The vaportravels to the compressor 74 where the working fluid is compressed. (Seeleg 90 of the refrigeration cycle in FIG. 4). The compressor 74 can be areciprocating, scroll or other type of compressor known in the art.After compression, the working fluid travels through a discharge line tothe condenser 76, where heat from the working fluid is dissipated to anexternal heat sink, e.g., the outdoor environment. (See leg 96 of therefrigeration cycle in FIG. 4). Upon leaving condenser 76, refrigerantflows through a liquid line to expansion device 75. As the refrigerantpasses through the expansion device 75, the second working fluidexperiences a pressure drop. (See leg 94 of the refrigeration cycle inFIG. 4.) Upon leaving expansion device 75, the working fluid flowsthrough the second fluid path of fluid-to-fluid heat exchanger 40, whichacts as an evaporator for the refrigeration cycle 70.

Conventional cooling systems for computer rooms or the like take upvaluable floor space. The present cooling system 10, however, can coolhigh-density heat loads without consuming valuable floor space.Furthermore, in comparison to conventional types of cooling solutionsfor high-density loads, such as computing rooms, cooling system 10conserves energy, because pumping a volatile fluid requires less energythan pumping a non-volatile fluid such as water. In addition, pumpingthe volatile fluid reduces the size of the pump that is required as wellas the overall size and cost of the piping that interconnects the systemcomponents.

The disclosed system 10 advantageously uses the phase change of avolatile fluid to increase the cooling capacity per square foot of aspace or room. In addition, the disclosed system 10 also eliminates theneed for water in cooling equipment mounted above computing equipment,which presents certain risks of damage to the computing equipment in theevent of a leak. Moreover, since the system is designed to removesensible heat only, the need for condensate removal is eliminated. As isknown in the art, cooling air to a low temperature increases therelative humidity, meaning condensation is likely to occur. If theevaporator is mounted on an electronics enclosure, for example,condensation may occur within the enclosure, which poses significantrisk to the electronic equipment. In the present system, the temperaturein the environment surrounding the equipment is maintained above the dewpoint to ensure that condensation does not occur. Because the disclosedcooling system does not perform latent cooling, all of the coolingcapacity of the system will be used to cool the computing equipment.

The disclosed cooling system 10 can handle varying heat loads withoutthe complex control required on conventional direct expansion systems.The system is self-regulating in that the pump 20 provides a constantflow of volatile fluid to the system. The flow regulators 32 operate soas to limit the maximum flow to each heat exchanger 30. This actionbalances the flow to each heat exchanger 30 so that each one getsapproximately the same fluid flow. If a heat exchanger is under “high”load, then the volatile fluid will tend to flash off at a higher ratethan one under a lower load. Without the flow regulator 32, more of theflow would tend to go to the “lower” load heat exchanger because it isthe colder spot and lower fluid pressure drop. This action would tend to“starve” the heat exchanger under high load and it would not cool theload properly.

The key system control parameter that is used to maintain all sensiblecooling is the dewpoint in the space to be controlled. The disclosedcooling system 10 controls the either the chilled water or the vaporcompression system so that the fluid going to the above mentioned heatexchangers 30 is always above the dewpoint in the space to becontrolled. Staying above the dewpoint insures that no latent coolingcan occur.

The foregoing description of preferred and other embodiments is notintended to limit or restrict the scope or applicability of theinventive concepts conceived by the Applicants. In exchange fordisclosing the inventive concepts contained herein, the Applicantsdesire all patent rights afforded by the appended claims. Therefore, itis intended that the appended claims include all modifications andalterations to the full extent that they come within the scope of thefollowing claims or the equivalents thereof.

What is claimed is:
 1. A cooling system for transferring heat from aheat load, the cooling system comprising: a two-phase working fluid; apump configured to increase the pressure of the working fluid withoutsubstantially increasing the enthalpy of the working fluid; anair-to-fluid heat exchanger in fluid communication with the pump and inthermal communication with the heat load; a fluid-to-fluid heatexchanger having a first fluid path in fluid communication with theair-to-fluid heat exchanger and the pump, and a second fluid path, thefirst and second fluid paths being in thermal communication with oneanother; a second heat transfer system in fluid communication with thesecond fluid path and comprising: a second portion of the fluid-to-fluidheat exchanger; a single phase working fluid; and a pump; wherein airpassing through the air-to-fluid heat exchanger causes at least aportion of the two-phase working fluid to change phase from a liquid toa gas within the air-to-fluid heat exchanger; and a controlleroperatively coupled to at least the second fluid path and configured toprevent condensation on the air-to-fluid heat exchanger by controllingthe amount of heat transferred to the second fluid path so that atemperature of the two-phase working fluid within the air-to-fluid heatexchanger is above a dew point temperature of the air passing throughthe air-to-fluid heat exchanger.
 2. The cooling system of claim 1,further comprising a flow regulator positioned between the pump and theair-to-fluid heat exchanger.
 3. A cooling system for transferring heatfrom a heat load to an environment, the cooling system comprising: afirst cooling cycle containing a two-phase working fluid; and a secondcooling cycle thermally connected to the first cooling cycle; whereinthe first cooling cycle comprises: a pump configured to increase thepressure of the working fluid without substantially increasing theenthalpy of the working fluid; an air-to-fluid heat exchanger in fluidcommunication with the pump and in thermal communication with the heatload; a second heat exchanger having a first fluid path for the workingfluid in fluid communication with the air-to-fluid heat exchanger andthe pump, and a second fluid path comprising a portion of the secondcooling cycle; wherein the first and second fluid paths are in thermalcommunication with one another; wherein the heat load causes at least aportion of the two-phase working fluid to change phase from a liquid toa gas within the air-to-fluid heat exchanger; and wherein the secondcooling cycle comprises a chilled water system in thermal communicationwith the environment and wherein the second cooling cycle is controlledto maintain a temperature of the two-phase working fluid entering theair-to-fluid heat exchanger above a dew point of air flowing through theair-to-fluid heat exchanger.
 4. A cooling system for transferring heatfrom a heat load to an environment, the cooling system comprising: aworking fluid pump configured to increase the pressure of a two-phaseworking fluid without substantially increasing the enthalpy of theworking fluid; an air-to-fluid heat exchanger connected to the pump andhaving a fluid path in thermal communication with the heat load; asecond heat exchanger having first and second fluid paths in thermalcommunication with one another, wherein the first fluid path providesfluid communication from the air-to-fluid heat exchanger to the pump,and wherein the second fluid path is adapted to thermally connect theair-to-fluid heat exchanger in the first fluid path to a chilled watercooling system that is in thermal communication with the environment;wherein air passing through the air-to-fluid heat exchanger transfersheat from the heat load and causes at least a portion of the workingfluid to change phase from a liquid to a gas; and a controlleroperatively coupled to the chilled water cooling system and configuredto maintain a temperature of the working fluid between the second heatexchanger and the air-to-fluid heat exchanger above a dew pointtemperature of the air passing through the air-to-fluid heat exchangerso that the cooling system removes only sensible heat from the air andthereby prevents condensation on the air-to-fluid heat exchanger.
 5. Aheat transfer system, comprising: a first heat transfer subsystemadapted to circulate there through a first working fluid, wherein thefirst working fluid is selected from the group consisting of:chlorofluorocarbons, hydrofluorocarbons and hydrochlorofluorocarbons,comprising: at least one air-to-fluid heat exchanger in thermalcommunication with a heat load; a pump configured to increase thepressure of the first working fluid without substantially increasing theenthalpy of the first working fluid; and at least a portion of a secondheat exchanger; a second heat transfer subsystem comprising: at least asecond portion of the second heat exchanger and a third heat exchanger;the second heat transfer subsystem adapted to circulate a second workingfluid there through, wherein the second working fluid is selected fromthe group consisting of: water, water-ethylene glycol, and waterpropylene glycol; and wherein air passing through the air-to-fluid heatexchanger causes at least a portion of the first working fluid toundergo a phase change from a liquid to a gas in the first heat transfersubsystem; and a system controller operatively coupled to the secondsubsystem and configured to prevent condensation on the air-to-fluidheat exchanger by maintaining the first working fluid leaving the secondheat exchanger above a dew point temperature of the air passing throughthe air-to-fluid heat exchanger.
 6. The system of claim 5, wherein theheat load is a room.
 7. The system of claim 5, wherein the heat load isan electronics cabinet.
 8. The system of claim 5, further comprising aflow regulator associated with at least one of the plurality ofair-to-fluid heat exchangers and which is adapted to control an amountof first working fluid flowing through the associated air-to-fluid heatexchanger.
 9. The system of claim 8, wherein the flow regulator isadapted to control the amount of first working fluid flowing through theair-to-fluid heat exchanger independently of fluid pressure.
 10. Thesystem of claim 8, wherein the flow regulator is adapted to maintain asubstantially constant flow of first working fluid through theair-to-fluid heat exchanger.
 11. The system of claim 8, furthercomprising a receiver in fluid communication with the first heattransfer subsystem for accumulating a portion of the first workingfluid.
 12. The system of claim 11, wherein the receiver is adapted toaccumulate a portion of the first working fluid based upon temperatureand/or heat load.
 13. The system of claim 8, further comprising a flowregulator associated with each of the plurality of air-to-fluid heatexchangers and which are adapted to limit an amount of first workingfluid flowing through each of the associated air-to-fluid heatexchangers.
 14. The system of claim 5, wherein the second heat exchangeris selected from the group consisting of: a tube-in-tube heat exchanger,a shell and tube heat exchanger and a plate and frame heat exchanger.15. The cooling system of claim 1, further comprising a working fluidreceiver in fluid communication between the fluid-to-fluid heatexchanger and the pump.
 16. The cooling system of claim 1, furthercomprising a working fluid flow regulating valve in fluid communicationbetween the pump and the air-to-fluid heat exchanger and a working fluidreceiver in fluid communication between the fluid-to-fluid heatexchanger and the pump.
 17. The cooling system of claim 3, furthercomprising a working fluid receiver in the first cooling cycle betweenthe second heat exchanger and the pump.
 18. The cooling system of claim3, further comprising a working fluid flow regulating valve in fluidcommunication between the pump and the air-to-fluid heat exchanger and aworking fluid receiver in fluid communication between the second heatexchanger and the pump.
 19. The cooling system of claim 4, furthercomprising a working fluid receiver in fluid communication between thesecond heat exchanger and the pump.
 20. The cooling system of claim 4,further comprising a working fluid flow regulating valve in fluidcommunication between the pump and the air-to-fluid heat exchanger and aworking fluid receiver in fluid communication between the second heatexchanger and the pump.
 21. The cooling system of claim 5, furthercomprising a working fluid receiver in the first heat transfer subsystembetween the second heat exchanger and the pump.
 22. The cooling systemof claim 5, further comprising a working fluid flow regulating valve influid communication between the pump and the air-to-fluid heat exchangerand a working fluid receiver in fluid communication between the secondheat exchanger and the pump.
 23. A cooling system for removing heat froma high density heat load, comprising: a first heat transfer systemcomprising: a two-phase working fluid; a plurality of air-to-fluid heatexchangers configured to transfer heat from the load to the workingfluid so that at least a portion of the working fluid changes phase froma liquid to a gas within at least one of the air-to-fluid heatexchangers; a working fluid flow regulator associated with at least oneof the plurality of air-to-fluid heat exchangers and configured to limitthe maximum working fluid flow to each air-to-fluid heat exchanger aworking fluid receiver configured to hold working fluid based on workingfluid temperature or cooling system load; a pump configured to increasethe pressure of the working fluid without substantially increasing theenthalpy of the working fluid; and a first portion of a fluid-to-fluidheat exchanger; wherein all of the first heat transfer system isarranged in fluid communication; a second heat transfer systemcomprising: a second portion of the fluid-to-fluid heat exchanger; asingle-phase working fluid; a pump; and wherein all of the second heattransfer system is arranged in fluid communication; wherein the firstheat transfer system is thermally coupled to the second heat transfersystem by the fluid-to-fluid heat exchanger; and a cooling systemcontroller monitoring the dew point temperature of air flowing throughthe air-to-fluid heat exchanger, and operatively connected to the secondheat transfer system to prevent condensation on the air-to fluid heatexchangers by maintaining the first heat transfer system working fluidentering the air-to-fluid heat exchangers at a temperature above the dewpoint temperature of the air flow.
 24. The system of claim 23, whereinthe air-to-fluid heat exchangers are located within an enclosure and thehigh density heat load is created by electronics within the enclosure,the enclosure having a forced air flow path across the electronics andthrough the air-to-fluid heat exchangers.
 25. The system of claim 24,wherein first heat transfer system is configured so that the workingfluid is cooled in the fluid-to-fluid heat exchanger and then flows tothe receiver and pump, and then flows through the regulating valves andthen into each air-to-fluid heat exchanger where at least a portion ofthe working fluid boils in each air-to-fluid heat exchanger, and thenthe heated working fluid returns to the fluid-to-fluid heat exchangerwhere it is once again cooled.
 26. The system of claim 23, wherein thesingle-phase working fluid is selected from the group consisting of:water, water-ethylene glycol, and water-propylene glycol.
 27. The systemof claim 23, further including a working fluid flow regulator associatedwith each air-to-fluid heat exchanger and each flow regulator configuredto limit the maximum working fluid flow to each air-to-fluid heatexchanger.